Free Expansion ( Unresisted Expansion ) Process

               The free expansion process is an irreversible non-flow process. A free expansion process occurs when a fluid is allowed to expand suddenly into a vacuum chamber through an orifice of large dimensions.

               Consider two chamber A and B separated by a partition. Since there is no expansion of the boundary of the system, because it is rigid, therefore no work is done. Thus, for a free expansion,
                                    Q1-2 = 0; W1-2 = 0 and dU = 0
                The following points may be noted regarding the free expansion of a gas:
1. Since the system is perfectly insulated so that no heat transfer takes place therefore the expansion of gas may be called as an adiabatic expansion.
2. Since the free expansion of the gas from the equilibrium state 1 to the equilibrium state 2 takes place therefore the intermediate state will not be in equilibrium states.
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